The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
1. Field of the Invention
The present invention includes chemically curable polymers used in binders for explosives and propellents. More particularly, the polymers include an ester component adjacent to a poly(oxyethylene) component to increase the hydrophilic and hydrolyzing properties of the polymer. The polymers are easily degraded to recover explosive/propellent chemical components.
2. Brief Description of the Related Art
Chemically cured binders currently used in explosives and propellants are difficult to degrade at the end of their life-cycle. With the lack of easy degradation, the recovery of valuable components of the energetic composition is hindered.
Several types of binders are known in explosives and propellants. Polybutadiene or polyether structures contain no readily degradable groups. Binders containing ester groups alone, such as polycaprolactone or carboxy-terminated prepolymers cured with epoxides, possess hydrolyzable ester groups, but the conditions for hydrolysis, i.e., time, temperature, are severe.
There is a need in the art to provide binders for energetic materials with prepolymers containing more readily hydrolyzable moieties in the backbone to improve the degradability of explosive and propellant binders. The present invention addresses this and other needs.
The present invention includes a degradable polymer for explosive and propellant compositions having increased hydrophilicity and hydrolyzability comprising an ester component within the structure of the polymer and a poly(oxyethylene) component within the structure of the polymer, wherein the ester component is located proximate to the poly(oxyethylene) component.
The invention further includes a degraded explosive polymer product formed by the process comprising the steps of providing a degradable polymer for explosive and propellant compositions having increased hydrophilicity and hydrolyzability comprising an ester component within the structure of the polymer and a poly(oxyethylene) component within the structure of the polymer, wherein the ester component is located proximate to the poly(oxyethylene) component, and reacting the degradable polymer with a degrading chemical composition.
The present invention includes a degradable polymer used to form binders in explosive and propellant compositions. The degradable polymers have increased hydrophilicity and hydrolyzability. Polymers containing hydrolyzable groups within the polymer chain are used to create the binders, while providing hydroxy or carboxy groups at the polymer chain ends. The degradable polymers have both an ester component and a poly(oxyethylene) component within the chain structure of the polymer, with the ester component and poly(oxyethylene) component sufficiently close together in the chain to allow the hydrophilic ether component to attract water close to the ester component and increase reactions between the water and ester component. The chemically cured hydrolyzable polymers create binders that are useful in energetic materials, such as explosives and propellants.
The ester component and poly(oxyethylene) component are sufficiently proximate to each other to allow the hydrophilicity of the ether component to influence the hydrolysis of the ester component. Preferably, the number of carbon atoms between the ester component and poly(oxyethylene) component ranges from about three carbon atoms or less, more preferably from about two carbon atoms or less, and most preferably approximately one carbon atom. By limiting the number of carbon atoms between the ester component and poly(oxyethylene) component, the distance between these components is restricted.
When combined within the structure of the polymer, the poly(oxyethylene) component may be located on either side of the ester component, away from the chain oxygen or on the side of the chain oxygen, or on both sides of the ester group.
The formed polymer of the present invention may comprise a hydroxy-terminated polymer or a carboxy-terminated polymer, formed by any suitable process. Hydroxy-terminated polymers may be formed by controlling the stoichiometry of the reagents, as shown in equation (1), below. With proper stoichiometry selected, having the diol reagent present in an amount of x+1 and the diacid reagent present in an amount of x, a hydroxy-terminated polymer is formed. 
with R representing a carbon or carbon heteroatom chain.
Additionally, hydroxy-terminated polymers may be formed, as shown in equation (2) below, with the diol reagent present in an amount of x+1 and the diacid reagent present in an amount of x. 
Formation of carboxy-terminated polymers of the present invention may be achieved as shown in equation (3) below, by adjusting the stoichiometry of the reagents of the reaction of equation (1). With the diol reagent present in an amount of x and the diacid reagent present in an amount of x+1, a carboxy-terminated polymer is formed. 
Additionally, carboxy-terminated polymers may be formed as shown in equation (4) below, by adjusting the stoichiometry of the reaction of equation (2). With the diol reagent present in an amount of x and the diacid reagent present in an amount of x+1, a carboxy-terminated polymer is formed. 
The prepolymers forming the binder comprise molecular weights suitable for processing, while enabling the formed binder to provide sufficient structural integrity to bind explosive and/or propellant compositions. The molecular weight of the prepolymers may range, for example, from about 2,000 to about 10,000; 2,500 to about 9,000; or 3,000 to about 8,000, with the proper molecular weight determinable by those skilled in the art for specific polymers and types of compositions.
Preferred hydroxy-terminated prepolymers include poly(PEG-400 adipate) having a polyethylene glycol component with a molecular weight of 400; poly(PEG-400 terephthalate) having a polyethylene glycol component with a molecular weight of 400; poly(PEG-400 poly(ethylene glycol) diacetic acid 604 ester) having a polyethylene glycol component with a molecular weight of 400 and an acid component with a molecular weight of 604; and poly(PCL-500 diol poly(ethylene glycol) diacetic acid 604 ester) having a polycaprolactone component with a molecular weight of about 500 and an acid component with a molecular weight of 604. Preferred carboxy-terminated prepolymers include poly(PCL-500 diol poly(ethylene glycol) diacetic acid 604 ester), having a polycaprolactone with a molecular weight of about 500 and an acid component with a molecular weight of 604. Of these, hydroxy-terminated poly(PEG-400 poly(ethylene glycol) diacetic acid 604 ester) and poly(PCL-500 diol poly(ethylene glycol) diacetic acid 604 ester) are most preferred.
When forming binders for energetic materials, the curing agent must be capable of reacting with the terminal groups on the prepolymers. When the terminal groups are hydroxyl groups, the di- or polyisocyanates are the preferred curing agents. Examples of suitable isocyanates include arylene polyisocyanates such as toluene diisocyanates; meta-phenylene diisocyanate; 4-chloro-1, 3-phenylene diisocyanate; methylenebis-(4-phenyl isocyanate); 1, 5-naphthalene diisocyanate; 3, 3xe2x80x2-dimethoxy -4, 4xe2x80x2-biphenylene diisocyanate; 3, 3xe2x80x2-diphenyl-4, 4xe2x80x2-biphenylene diisocyanate; triphenylmethane triisocyanate; and alkylene poly-isocyanates such as methylene; ethylene; propane-1, 2; butane-1, 3; hexane-1, 6 and cyclohexane-1, 2 diisocyanates. Mixtures of poly-isocyanates may also be used. ISOPHORON diisocyanate and Desmodur N-100 isocyanate curing agent, a commercial product of the Bayer Corp., Pittsburgh, Pa., are most often used. When the terminal groups are carboxyl groups, the useful curing agents include polyfunctional epoxides. The formed prepolymers possess a functionality suitable for curing with isocyanates or epoxides, with a preferred functionality of from about 1.7 to about 2.3, more preferably with a functionality of approximately 2.
Degradation of the polymers or formed binders may be performed by contact with a basic or acidic degrading chemical composition, such as a dilute base or acid composition. Contact between the polymers and degrading composition is enhanced with agitation, such as stirring or mixing. Dilute base or acid compositions include suitable concentrations, such as from about 2.0 N or less, 1.5 N or less, or 1.0 N or less, with the proper concentration for a particular polymer or binder determinable by those skilled in the art. Once the degrading composition is in contact with the polymer, the hydrophilic nature of the poly(oxyethylene) component facilitates drawing the polymer into the dilute base or acid. With the ester component located proximate to the poly(oxyethylene) component, the hydrolyzability of the polymer substantially improves during contact.